The present invention relates to novel compositions based on epoxides and polyamides, and more particularly, it relates to compositions prepared from epoxide resins and polyamide oligomers, processes for their preparation, and their uses.
It is known that epoxide resins can react with polyamides and vice versa. Thus, polyamides can be cross-linked with small quantities of polyepoxides. Conversely, it is possible to produce thermosetting polymers by treating epoxide resins with small quantities of certain polyamides, but in this case conventional methods of cross-linking epoxide resins are involved.
Cross-linking of epoxide resins by polyamides is described in the literature, particularly Lee and Neville, "Handbook of Epoxy Resins", McGraw-Hill, New York 1967. The so-called "polyamide" compounds usually employed as hardeners in epoxide resin formulations are generally amorphous and of low molecular weight. They are, for example, amidopolyamides produced by the reaction of dimerized fatty acids with an excess of diamine or polyamine.
Since dimerized fatty acids are mixtures of isomers of several diacids, with a poorly defined structure, produced by dimerization of mono- or polyunsaturated fatty monoacids, the resultant polyamides themselves have a poorly defined structure and are amorphous. Because of their high content of amine groups (more than two amine groups per molecule), they cross-link epoxide resins, but the amide groups which they contain do not play a dominant role in the final properties of the product. Finally, because of their amorphous nature and their low softening point, these polyamides react with epoxide resins at low temperature.
High molecular weight semi-crystalline polyamides have been employed as additives in epoxide resin formulations to improve some of their properties but, in this case, these polyamides really act as fillers. Moreover, European Patent Application No. 83 1,003,311-6 (Publication No. 0085324) describes polyamide compositions prepared by anionic polymerization of at least 75% lactams with approximately 25% of an epoxide compound, but the process claimed only applies to certain polyamides, that is, those derived from lactams and, furthermore, as it involves anionic polymerization, it has all the disadvantages thereof.